I have had nickel silver track in my backyard since 1993 it is still in great shape. My oldest track is Micro Engineering NS, code 250, http://microengineering.com/products_rail.htm. I also have some Llagas Creek NS, code 250 that is about 6 years newer. http://www.llagastrack.com/#railmaterials. They both work great. I still run some track powered trains but I find myself increasingly preferring R/C battery operation. When I do want to run track power I just brush the dirt and leaves off the track and find that I don't have to scrub the rail until it's shiny to get it to conduct the current.

My track just floats and I use decomposed granite for ballast. (For a backwoods, narrow gauge look).

You use rechargeable batteries in the engine to power the motor and control the voltage with a radio receiver and transmitter. I would advise sticking with track power to begin. If you go to a club meet someone will probably be using radio control and they can show you how their system works.

Nowhere near that simple. With battery power, you need some kind of on-board throttle to control the speed and direction. (i.e., Airwire, Aristo-Craft Revolution, etc.) Those systems will run you anywhere from $100 - $300 per loco depending on the features it has and if it has sound), and that does not including the cost of the transmitter, battery or charger. In most cases, you'll have to do some level of modification to the locomotive itself to install it. It's definitely not anything I would remotely recommend an 11-year-old take on.

My recommendation is to stick with track power, until you grasp the basics of outdoor model railroading. There is enough to learn when you are getting your track down and running your first train.

There are a lot of other options out there for other types of power: battery, battery/radio control, DCC, live Steam. Within each of those are other choices. Don't jump into the other options until you have talked to people who use them. There are advantages and disadvantages to all these power sources, including track power. You need to discover what is best for you, so you don't spend money on something that you will later wish you hadn't.

I have converted three of my engines to battery/RC. I did it so that I can run as a guest on other layouts that do not have track power. My present layout (my second) has been down since 1994 and I don't need battery/RC for it. My first one was in Denver (1985-1993). For the trains that I have run on my layouts, I have never thought that I needed more that track power. I run one train at a time, with up to two made up trains on passing sidings. If I double or triple head, I run similar engines so that the motors and gearing match. Such as a USAtrains F3 ABA diesel set, or two identical LGB engines.

There is plenty of time to change your power requirements. At the start, KEEP IT SIMPLE.